This invention relates to a method and improved apparatus for automatically locating the QRS portion of an electrocardiographic signal. More specifically, it relates to the use of an adaptive peak detector circuit which automatically locates the QRS portion of an applied electrocardiographic signal.
Typically, in the case of a normal heart, the amplitude of the QRS portion of the electrocardiographic signal predominates over the other portions, i.e., the P and T portions, of the electrocardiographic signal. Accordingly, many conventional methods of detecting the QRS portion of an electrocardiographic signal use some form of level comparator in conjunction with Schmitt trigger techniques to generate a synchronization (sync) signal whenever the amplitude of the applied electrocardiographic signal exceeds a predetermined level. However, these techniques are often not useful in the case of an abnormal heart where the QRS portion of the electrocardiographic signal is often obscured by the irregularities of the T portion of the electrocardiographic signal.
Furthermore, the conventional type of QRS detector is somewhat limited in its ability to automatically operate over the wide dynamic range of expected input electrocardiographic signals. Typically, the amplitude of the QRS portion of an electrocardiographic signal varies between 150 microvolts to 1.5 millivolts. Often, a manual adjustment is required to account for patient to patient variations in QRS signal strength.
Another limitation inherent in some of the conventional QRS detectors is the inability to operate with electrocardiographic signals in which the QRS portion is of negative polarity.
The above limitations and drawbacks associated with conventional types of QRS detectors are undesirable in certain applications. For example, it is often desired in certain medical equipment, in the presence of an input signal which varies in amplitude and polarity, to accurately establish a time reference and generate a sync pulse upon detection of the QRS portion of an electrocardiographic signal.
An example of such medical equipment is illustrated in copending application Ser. No. 854,537, filed Nov. 25, 1977, entitled, "Method and Apparatus for Characterizing Blood Flow through the Heart", assigned to the assignee of the present invention, and incorporated herein by reference. As described therein, a QRS detector is used to establish a time reference and generate a pulse used to synchronize a cathode ray tube display of the output of the left ventricle of the heart.
Accordingly, it is an object of the invention to provide a method for automatically locating the QRS portion of an electrocardiographic signal.
It is a further object of the invention to provide improved apparatus for automatically detecting the QRS portion of an electrocardiographic signal and generating a corresponding synchronization pulse.
It is still a further object of the invention to provide apparatus for automatically detecting the QRS portion of an electrocardiographic signal which varies in amplitude and polarity.